1. Field of the Invention
This invention relates to an optical reading apparatus such as a bar code reader for reading a linear recording medium such as a bar code and converting it into a display signal, and more particularly to an optical reading apparatus such as a bar code reader which prevents reading of a linear recording medium from being disabled by a regular reflection condition which occurs upon reading of the linear recording medium.
2. Description of the Related Art
A bar code reader which reads a bar code performs conversion processing of the thus read bar code such as decoding and outputs a resulted signal as a required display signal conventionally includes a light emitting element for emitting light to an information recording surface on which a bar code is printed, a light receiving element for receiving reflected light from the information recording surface and generating a bar code read signal, a signal processing section for performing conversion processing of the bar code read signal such as amplification, binary digitization, decoding and so forth and outputting a resulted signal as a required display signal, and a driving section for driving the light emitting element.
FIG. 10 shows, in block diagram, an example of a construction of a known bar code reader of the type described above. Meanwhile, FIGS. 11(a) and 11(b) are signal waveform diagrams illustrating conditions of signals at several portions of the known bar code reader when a bar code is read, and FIG. 12 is a schematic sectional view showing the known bar code reader during use.
As seen from FIGS. 10 and 12, a bar code 61 is printed on an information recording surface 61a. A light emitting element 62 formed from a light emitting diode (LED) or a like element is located in the proximity of a reading portion (end portion) of the bar code reader, and a light receiving element 63 formed from a photodiode array or a like device is located a little rearwardly of the light emitting element 62 at the reading portion (end portion) of the bar code reader. Light emitted from the light emitting element 62 is reflected by the information recording surface 61a on which the bar code 61 is printed, and is then condensed by a lens 63a and introduced into the light receiving element 63 by way of a pin hole plate 63b. The output of the light receiving element 63 is connected to the input of an amplifier 64, and the output of the amplifier 64 is connected to the input of a binary digitizing circuit 65. The output of the binary digitizing circuit 65 is connected to the input of a decoding circuit 66, and the output of the decoding circuit 66 makes the output of the bar code reader. In this instance, the amplifier 64, the binary digitizing circuit 65 and the decoding circuit 66 constitute a signal processing section. A driving section 67 supplies driving power for driving the light emitting element 62.
Operation of the bar code reader having the construction described above will be described below with reference to FIGS. 11(a) and 11(b). Now, if a user grasps the bar code reader in a hand so that the reading portion (end portion) of the bar code reader may be opposed to the information recording surface 61a on which the bar code 61 is printed, then light emitted from the light emitting element 62 and irradiated upon the information recording surface 61a on which the bar code 61 is printed is reflected by the information recording surface 61a, and the reflected light is supplied to the light receiving element 63. Upon reception of the reflected light, the light receiving element 63 generates a bar code read signal and supplies the bar code read signal to the signal processing section constituted from the amplifier 64, the binary digitizing circuit 65 and the decoding circuit 66. In the signal processing section, the bar code read signal is first amplified to a predetermined level by the amplifier 64 and then converted into a binary signal by the binary digitizing circuit 65. Then, the binary signal is decoded by the decoding circuit 66, and the decoded signal from the decoding circuit 66 is outputted as a display signal from the bar code reader. In this instance, when such a pattern of the bar code 61 as seen at the top stage in FIG. 11(a) is read, the amplified bar code read signal waveform A appearing on the output side of the amplifier 64 exhibits such a form of pulses corresponding to the bar code 61 as seen at the middle stage in FIG. 11(a), and the binary signal waveform B appearing on the output side of the binary digitizing circuit 65 exhibits such a binary signal corresponding to the bar code 61 as seen at the lower stage in FIG. 11(a).
It is to be noted that light to be irradiated from the bar code 61 upon the information recording surface 61a on which the bar code 61 is printed may be continuous light or intermittent light which has a predetermined timing pattern.
By the way, in the known bar code reader described above, in reading the information recording surface 61a on which the bar code 61 is printed, when the light irradiation angle at which light is irradiated from the light emitting element 62 upon the information recording surface 61a on which the bar code 61 is printed and the light receiving angle at which light reflected from the information recording surface 61a on which the bar code 61 is printed is inputted to the light receiving element 68 satisfy individual particular requirements, a condition wherein most of light irradiated upon the information recording surface 61a on which the bar code 61 is printed is received as reflected light by the light receiving element 68, that is, a condition wherein the amount of light received by the light receiving element 63 exhibits a sharp peak condition, occurs. This condition is normally called regular reflection condition. When such regular reflection condition is entered, a large amount of light is introduced into the light receiving element 63 at a time, and the bar code read signal extracted from the light receiving element 63 exhibits a sudden variation to a very large amplitude. Thus, the amplifier 64 at the next stage is saturated by the bar code read signal of the large amplitude thus inputted thereto, and consequently, at least part of bar code components of the bar code read signal is lost as seen from the signal waveform C of FIG. 11(b). If such bar code read signal is inputted to the binary digitizing circuit 65, the binary digitizing circuit 65 cannot extract the bar code components from within the bar code read signal due to the loss of at least part of the bar code components. Consequently, the binary digitizing circuit 65 cannot generate a binary signal corresponding to the bar code components as seen from the signal waveform D of FIG. 11(b). Further, since the binary signal supplied from the binary digitizing circuit 65 to the decoding circuit 66 does not include at least part of the binary signal corresponding to the bar code components, the decoding circuit 66 cannot generate a decoded signal corresponding to the bar code components and accordingly cannot output a required display signal from the bar code reader.
Consequently, with the known bar code reader described above, when such a regular reflection condition as described above occurs, a reading operation of the information recording surface 61a on which the bar code 61 is printed is performed repetitively until bar code components are read, that is, until a required display signal is outputted from the bar code reader.
The known bar code reader described above, however, is disadvantageous in that, when a regular reflection condition occurs, much time is required for accurate reading of the bar code 61 because a reading operation of the information recording surface 61a on which the bar code 61 is printed must be performed repetitively until a required display signal is outputted from the bar code reader. The known bar code reader is further disadvantageous in that, particularly where a user of the bar code reader is inclined to perform a reading operation of the bar code 61 in a condition in which a regular reflection condition occurs comparatively likely, much more time is required to accurately read the bar code 61.